This is a followup question after

How to Make BIOS/UEFI Flash Drive with Full Disk Encryption

I have followed the answers in this question and created an encrypted full installation of Ubuntu 20.04 in an USB flash drive that booted from either from BIOS or from UEFI configured computers.

Over time I have used this USB flash drive installed Ubuntu in a BIOS only computer and kept it updated with security and other updates. Now the UEFI computer won't boot from this USB drive. When I select Ubuntu from the GRUB it shows me the error:

error file '/vmlinuz-5.8.0-48-generic' not found.
you need to load the kernel first. 

This specific kernel is not installed as it was superseded by newer kernels during security and other updates.

How do I regain the UEFI boot functionality for this USB based Ubuntu installation?

I installed Ubuntu 18.04 using the "Something else..." option on a laptop with a single HDD that came with Windows 10. During installation I deleted all the partitions except the EFI partition. Then I created a / root file-system partition and a /home partition. All went well.

Except now I have an extra Windows entry in the UEFI boot menu that gets picked up by Grub. I can manually edit /etc/default/grub to hide the now defunct Windows boot option, but I want to get rid of the entry in the EFI system as well. How do I get rid of this final vestigial remnants of Windows?

I have firewalld working following the answer Firewalld does not start at boot.

I have hybrid-sleep working following How do I use pm-suspend-hybrid by default instead of pm-suspend?

However, if firewalld is active and I close the lid to initiate hybrid-sleep, then the system freezes with black screen. If I initiate normal sleep via power cog menu > Suspend then the computer suspends fine. I can also get the computer to hybrid-sleep if I stop the firewalld service before putting the computer to hybrid-sleep.

My computer is running Ubuntu 16.04.2 LTE with HWE.

My question is how do I prevent the conflict between firewallD and hybrid-sleep?

Thanks

I have installed firewalld and uninstalled ufw with the following commands:

sudo apt install firewall-applet
sudo systemctl start firewalld
sudo systemctl enable firewalld

It works but does not start on its own on restart.

$ sudo systemctl status firewalld.service
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/lib/systemd/system/firewalld.service; enabled; vendor preset
Active: inactive (dead)

May 10 18:39:03 Yyyy systemd[1]: Stopped firewalld - dynamic firewall daemon. lines 1-5/5 (END)

My laptop is running Ubuntu 16.04 LTS.

The output of sudo systemctl status iptables.service:

● iptables.service
Loaded: not-found (Reason: No such file or directory)
Active: inactive (dead)

Iptables is installed. The output of dpkg -s iptables

Package: iptables
Status: install ok installed
Priority: important
Section: net
Installed-Size: 1624
Maintainer: Ubuntu Developers <[email protected]>
Architecture: amd64
Version: 1.6.0-2ubuntu3
Depends: libxtables11 (= 1.6.0-2ubuntu3), libc6 (>= 2.14), libnfnetlink0
Description: administration tools for packet filtering and NAT
 iptables is the userspace command line program used to configure
 the Linux packet filtering ruleset. It is targeted towards system
 administrators. Since Network Address Translation is also configured
 from the packet filter ruleset, iptables is used for this, too. The
 iptables package also includes ip6tables. ip6tables is used for
 configuring the IPv6 packet filter
Homepage: http://www.netfilter.org/
Original-Maintainer: iptables devel team <[email protected]>

I tried sudo firewalld-cmd --runtime-to-parmanent but it does not help firewalld start at boot.

Thanks